Many technological advances have resulted in the provisioning and delivery of telephony services over packet networks. In past circuit switched telephony networks, a user may be presented with dial tone played out by the network upon taking a phone off-hook. In packet networks, dial tone is emulated by a device local to the user. Often, the user's modem or other residential system emulates the dial tone previously provided by circuit switched networks. This is necessary because dial tone indicates the availability of telephony services to the user.
When telephony service is not available in a circuit switched network, the user is presented with a fast busy signal from the network indicating that no connections are available for a call. Likewise in a packet network, an emulated fast busy signal may be presented to the user during congestion conditions. However, many emergency service regulations require packet telephony providers to provide the ability to override congestion controls when a caller dials such services. Unfortunately, by emulating a fast busy signal upon a user going off-hook, the user is discouraged from placing the call to an emergency service.